One of the goals of electricity metering is to accurately measure the use or consumption of electrical energy resources. With such measurements, the cost of generating and delivering electricity may be allocated among consumers in relatively logical manner. Another goal of electricity metering is help identify electrical energy generation and delivery needs. For example, cumulative electricity consumption measurements for a service area can help determine the appropriate sizing of transformers and other equipment.
Electricity metering often involves the measurement of consumed power or energy in the form of watts or watt-hours. To this end, meters include voltage sensors and current sensors that detect, respectively, the voltage and current delivered to the load. In most cases, the purpose of the voltage sensor is to provide a measurement signal that represents a scaled version of the voltage waveform delivered to the load. Similarly, a current sensor provides a measurement signal that represents a scaled version of the current waveform delivered to the load.
The current measurement in a utility meter can be challenging because a high accuracy is required, and common current sensor technologies can be susceptible to various sources of error. Present metering technologies involve current transformers, or CTs. Existing CT designs are prone to saturation and may distort, causing error especially in a DC magnetic field or when measuring current through a half wave rectified load. Such errors can result in inaccurate measurements, and hence lost revenue.
Moreover, it is known to tamper with meter operation by applying a strong magnet to the meter with the purpose of saturating the CT, thereby resulting in inaccurate measurements. Similarly, it is known to apply half-wave rectification to a load in order to saturate the CT of the meter. Various efforts have been made to thwart such tampering attempts. For example, it is known to provide a metal shield around the CTs of the meter to prevent saturation due to an externally applied permanent magnetic field. However, this adds cost and weight to the meter, and is not effective against other sources of error.
There is a need, therefore, for a current sensor arrangement that favorably improves upon one or more of shortcomings of existing transformers, for example, by providing sufficient accuracy under various circumstances while reducing production cost.